This invention relates to tantalum powders and to anodes prepared therefrom, and specifically to powders capable of producing anodes improved in electrical capacitance and, in one embodiment, powders having improved flow characteristics.
The use of tantalum powders for the preparation of electrodes in electrolytic capacitors is well known. Such electrodes are made by pressing the tantalum powder to form a coherent compact, sintering the compact and subsequently forming a dielectric film on the sintered product.
In such capacitors it is desired to have as high a specific capacity CV/g. as possible. U.S. Pat. No. 3,418,106 discloses an agglomerated tantalum powder crushable as tantalum which when fabricated into an electrode provides enhanced specific capacity. The agglomerated tantalum powder described in this patent also has improved flow characteristics as compared to prior powders.
U.S. Pat. No. 3,825,802 discloses improvements in various properties of tantalum capacitors, including specific capacity, by the addition to the tantalum of any of several "dopants", including phosphorus. The range of dopant disclosed is from 0.47 to 2.71 atomic percent which, for phosphorus is equivalent to from about 800 to 4600 parts per million and the improvement in specific capacity (for nitrogen, the preferred species) ranges from about 2% (at the lower end of the range) to about 6.3% (at the upper end) when the anode is sintered at 1900.degree. C.